REPORT ON THE OPHIUROIDEA. 113 



In respect to disk scales and radial shields the arrangement resembles that of Ophio- 

 pholis (especially in Ophiactis asperula), though other species (e.g., Ophiactis cusp'ulata) 

 have much larger and stouter scales. There is a resemblance likewise in the peristomial 

 plate which is wanting (Ophiactis kroyeri), or is a mere thin crust (Ophiactis savignyi), 

 or is small and linear (Ophiactis asperula). The genital plate is usually very stout, 

 though long, slender, and cylindrical in Ophiactis kroyeri, and has attached to it a 

 considerably shorter genital scale. The arm bones are discoid and delicate, with thin 



wings. 



Table of Species of Ophiactis. 



1st Type. The number of mouth papilla? increase with age. 



Six to seven short, thick, blunt rough arm spines. Young usually with six ' 

 arms; adult often with only five. Commonly two mouth papillae on 

 each side ; rarely more. Upper arm plates microscopically tuberculous, 

 swollen, usually w T ith a faint lobe on the outer edge. Radial shields [ Ophiactis savignyi. 

 large, scarcely diverging, nearly or cpuite touching. Side mouth 

 shields nearly or quite meeting at their outer ends. Numerous disk 

 spines, 



Radial shields narrow, oval, and separated. Upper arm plates wider than long, \ 



with lateral sides re-enteringly curved. Under arm plates broader than > Ophiactis affinis. 

 long, and cleanly curved without, . . . . . ; 



The adult (var. quinqueradia) has five arms; upper arm plates transverse oval, \ 



and not thickened; three or even four mouth papillae on a side. The \ Ophiactis mulleri. 

 young is like Savignyi (six arms), but has no lobe on upper arm plate, . ) 



Skin thick and much obscuring the scaling and mouth shields. Radial shields 

 narrow and small. Five short, thick, blunt, flattened arm spines, 



2nd Type. The number of mouth papilla seems never to vary. 

 Small radial shields, just touching without, widely diverging inward, four stout " 

 and blunt, but cylindrical and tapering, arm spines. Disk scales curved 

 and regularly imbricated. Upper arm plates fan-shaped and symmetrical. 

 A few disk spines. One mouth papilla, ..... 



Differs from preceding in disk scales less overlapping ; two mouth papillae on I , 



each side, and side mouth shields not meeting without, . . . J 



Six arms ; two mouth papillae on each side. Radial shields proportionately \ 



larger than in Ophiactis halli, upper and under arm plates longer, and > Ophiactis loricata. 

 disk scales less regular. Side mouth shields not meeting without (young?) / 



Differs from Ophiactis halli in under arm plates, from loricata in fan shaped ) _ , . 



. . t Ophiactis tiimam. 



upper arm plates, . . . . . . . ) ■* 



Near Ophiactis halli, but only three arm spines; no disk spines. Teeth lobed. \ . 



Side mouth shields not meeting without, . . . . . f 



Disk scales distinct and naked, without spines. Three stout, blunt, tapering, \ 



cylindrical arm spines. One large flat mouth papilla on each side. Teeth > Ojthiactis flexuosa. 

 lobed. Five arms, . . . . . . .1 



Differs from Ophiactis halli in arched disk with radial shields not well dis- ) 



1 'u'acfis /•//•■ ne. 



} Ophiactis resiliens. 



■ Ophiactis halli. 



tinguished from other scales; and in transverse oval upper arm plates, 



■ Ophia 



